Circuit interrupter



June 16, 1936. H. l.. RAwLxNs CIRCUIT INTERRUPTER Filed Aug. 25, 1953wenn 1 N A@ gTNESSES:

' ATToR EY Patented June 16, 1936 UNITED STATES CIRCUIT INTERRUPTERHerbert L. Rawlins, Wilkinsburg, Pa., assignor to Westinghouse Electric& Manufacturing Company, East Pittsburgh, Pa.,

Pennsylvania a corporation of Application August 25, 1933, Serial No.686,760

19 Claims.

My invention relates to circuit interrupters and particularly to highvoltage explosion fuses.

One object of my invention is to provide a rellable high voltageexpulsion fuse that shall be simple in design, more economical tomanufacture, and more satisfactory and reliable in operation than thepreviously known devices of this type.

Another object of my invention is to provide an improved refill elementfor use with expulsion fuses, my improved refill element to beinexpensive to manufacture and simple to install.

A further object of my invention is to provide an improved high voltageexpulsion fuse which shall include at least two separate arc passagesand means for establishing an are in each of the passages, the arcinterrupting capacity of the two passages being different in order thatthe fuse may be equally effective for both high and low values of arccurrent.

A further object of my invention is to provide an improved circuitinterrupter wherein a biased contact member is held against its biasingforce by a fusible element which possesses considerable mechanicalstrength but which is fusible upon the occurrence of relatively moderateoverloads to permit the biasing means to cause the opening of theinterrupter.

vA further object of my invention is to provide an improved high voltageexpulsion fuse which shall utilize a fusible element having suflicientlyvlarge physical dimensions to prevent any injury thereto as a result ofcorona formation, and which shall, at the same time, be operable toeffect the opening of the controlled circuit when relatively lowmagnitude currents flow therethrough.

A further object of my invention is to provide an improved fusibleelement for use with electrical apparatus. My improved fusible elementto have suicient thermal capacity to prevent the operation thereof uponthe occurrence of transient overloads of large magnitude and to beoperable upon the occurrence of continued overloads of small magnitude.

A further object of my invention is to provide an improved circuitinterrupter which shall be operable upon the actuation of thermallyresponsive means which includes a current carrying heater and means forincreasing the normal heating effect of the heater upon the occurrenceof predetermined conditions.

A still further object of my invention is to provide an improvedexpulsion fuse structure which shall include a means for closing one endof the fuse tube and electro-responsive means for opening that end ofthe fuse tube upon the occurrence of predetermined conditions.

One field for immediate application of my invention is in connectionwith high voltage potential transformer fuses that utilize boric acid asthe source of arc extinguishing gas, and I shall hereinafter describe anembodiment `of my invention as applied to such devices without, however,in any way intending to restrict the scope of my invention except asindicated in the appended claims.

In this type of fuse, a short fusible link is connected to the lower endof a movable rod or plunger, the other end of the rod being affixed to apiston member of conductingl material which is disposed within aninsulating tube and is biased upwardly by a coil spring. A flexibleconducting shunt disposed Within the coil spring completes theelectrical circuit to the stationary contact. Upon the fusing of thelink, the rod moves upwardly under the influence of a biasing spring.and establishes the arc within a chamber that is lined with boric acid.The boric acid being decomposed and the resulting outwardly flowingvapor, substantially all of which is superheated steam, extinguishes thearc.

The fuse is restored to an operative condition following each circuitinterrupting operation by the removal and replacement of the refillelement which includes the boric acid lining for the arc passage, themovable plunger, and the fuse assemblage.- From this, it is immediatelyapparent that the refill operation consists in the replacing of all ofthe parts which are subjected to the action of the arc, therebycontinuing reliable operation of the device.

The fusible element which is used in this type of circuit interrupter issubjected to very exacting operating requirements. In order to securesatisfactory operation of the fuse, it is necessary that the plunger bemoved at a comparatively rapid rate thus necessitating the use of arelatively powerful actuating spring. The entire force of this springmust be opposed by the fusible link itself and at the same time, thelink must be capable of fusing when relatively low current flowstherethrough. This last requirement is particularly important incircuits such as potential transformer circuits wherein the maximumcurrent carried usually does not exceed one-half ampere. must haveconsiderable mechanical strength, it must be capable of opening thecircuit when comparatively low magnitude currents ow therethrough, andat the same time, it must have suiiicient physical dimensions to preventany injury theretc as a result of corona formation.

Heretofore there has been no satisfactory means for accomplishing theserequirements and consequently entirely no satisfactory high voltage fusehas been available for use on circuits having a normal line current ofless than amperes. A fuse embodying the features of my invention,however, meets all of these requirements Thus, thpe` fusible link andpermits the satisfactory operation of a high voltage fuse upon overloadcurrents as low as one-tenth ampere, this increased range ofsatisfactory operation being made possible by the novel means which Iemploy for causing the fusing of the link which holds the movableplunger in the closed circuit position against the spring biasing means.

The features of my invention which I believe to be new are particularlypointed out in the appended claims. For a fuller understanding of thoseprinciples and the best mode of applying the same, reference may be hadto the accompanying drawing, in which Figure 1 is a side elevationalView, partially in section, of an expulsion fuse embodying the principalfeatures of my invention.

Fig. 2 is an enlarged sectional view of a reiiill element for use withthe expulsion fuse shown in Fig. 1.

Fig. 3 is a fragmentary sestional view similar to Fig. 2 showing amodified form of refill unit.

Figs. 4 and 5 are end elevations of the reiill unit shown in Fig. 2.

Fig. 6 is an enlarged detailed view of the plunger assemblage shown inFigs. 1 and 2, and

Figs. 7, 8 and 9 are detail views showing the improved heating deviceutilized in this embodiment of my invention.

The expulsion fuse shown in Fig. 1 includes a cylindrical fibre tube I,having relatively heavy side walls and threaded ends 3 and 5, and twotubular terminal members 1 and 9 of conducting material which havethreaded portions II and I3, respectively, for engaging the threadedends 3 and 5 of the main iibre tube l. The outer surface of each of theterminal members 1 and 9,

which are substantially cylindrical in form, is utilized for engagingsuitable contact jaws (not shown). The upper terminal member 1 isprovided with a second internally threaded portion I5 for engaging anannular member I1 which is utilized for supporting one end of theoperating spring I9. The upper end of the fuse I is closed by means of acap member 2I having a threaded internal portion 23 which cooperateswith a similarly threaded portion 25 on the upper support member 21 forthe operating spring I9.

The working parts of the fuse include the main operating spring I9, oneend of which engages a threaded portion 29 on the upper support member21, the flexible conducting shunt 3I disposed within the main operatingspring I9 and electrically connected to the upper spring supportingmember 21 and the piston member 33 by means of suitable screws 35, andthe refill element 31 which engages the piston member 33. The lower endof the operating spring I9 engages a threaded portion 39 on the pistonmember in substantially the same manner that the upper end engages thesupport member 21.

The preferred form of the refill element 31 is shown particularly inFig. 2. It includes a bre tube 4I, having side walls of considerablemechanical strength and a threaded end 42 for engaging the threadedmetallic ferrule 44. The fibre tube 4I is lined for the greater part ofits length with a cylindrical lining member 43 composed of compressedboric acid. The boric acid lining 43 has a cylindrical passage 45,through the central portion thereof for accommodating the rod or plunger41, and is further provided with a second passage 49 extendingtherethrough of considerably smaller cross sectional area than thecentral passage 45.

, taining rivet 1I.

A threaded fibre plug 5I having an opening 53 therethrough is providedfor engaging the upper end of the boric acid lining 43. The lower end ofthe central passage 45 terminates in a conical throat 55, the lowerportion of which is dened by a fibre plug 51, it being desirable toprovide material of greater mechanical strength than boric acid forlining those portions of thel arc passage where the thickness of thelining becomes small. The ferrule 44 has a threaded portion 59 forengaging the threaded end 42 of the fibre tube 4I and is provided withan annular shoulder 6I for engaging the end of the fibre plug 51. Thecentral opening 63 through the ferrule 44 forms a continuation of thecentral passage 45 and the throat 55.

The cylindrical plunger or rod member 41 is preferably constructed ofcopper; the lower end has a slotted opening 55 therein for engaging oneend of the liat fusible strip 61, a soft metal rivet 69 being providedfor rigidly ailixing the fusible element 61 thereto. The other end ofthe fusible link 61 is soldered within a slot 13 in the copper rivet 1I,which is adapted to engage the disk member 15 to hold the plunger 41against movement under the biasing influence of the spring I9. The diskmember in turn abuts against; the annular shoulder 6I in the ferrule 44of the refill element.

The upper end 11 of the plunger Vrod 41 is threaded for engaging thepiston member 33, and is provided with a positioning pin 19 extendingtherethrough substantially at right angles to the longitudinal axis ofthe plunger. This pin, as is shown particularly in Figs. 2 and 4,cooperates with two diametrically opposed slots BI in the top portion ofthe fibre tube 4I of the refill unit in order to prevent rotation of theplunger with respect to the other parts of the refill unit during therefilling operation.

In both forms of refill unit, a wire 83, of somewhat smaller crosssectional area than the cross sectional area of the smaller passage 49through the boric acid lining 43, is securely afiixed to the upper endof the plunger rod 41 and extends down into the smaller passage 49 whereit slidably engages a similar wire 85 extending upwardly into thesmaller passage for about one-third of its length. The lower end of thewire 85 is retained in position within a recess 81 in the libre throatmember 51.

The retaining disk member 15 which is utilized for holding the plungermember 41 against the biasing force of the operating spring I9 is shownparticularly in Figs. 7, 8 and 9. The disk 15 is preferably constructedof a non-metallic resistance material such as carbon or carborundum, andis provided with a central opening 89 to permit the passage therethroughof the shank portion of the rivet 1I, and a pair of annular metalportions 9| and 93 electroplated thereon. The outer plated portion 9| isadapted to engage the annular shoulder 6I on the ferrule 44 in order toprovide a good electrical connection between the disk and the ferrule,and the inner plated portion 93 is adapted to engage the plunger re-'Ihe disk 15 is used for supplying heat to the retaining rivet 1I inorder to cause the fusion of the fusible link 61 which is soldered inthe slot 13 therein. This arrangement is most suitable for use on verylow current circuits, due to the fact that the disk itself possessesconsiderable inherent resistance to the flow of an electric current; itdoes permit, however, very accurate calibration of the device.

I prefer to'use one of the lead bismuth alloys, the proportions of whichclosely approximate those of the eutectic alloy of those metals, for thefusible link 61. These alloys have very sharp melting points, usually inthe neighborhood of 80 to 126 C., and permit very close calibration ofthe thermally responsive element.

In the modification shown in Fig. 3, the resistance disk is parallelledby a second fusible element 95 soldered at one end to the ferrule 44 andat the other to the retaining rivet 1I. This arrangement results in thesecuring of a parallel path current-carrying heater which is operableupon the occurrence of predetermined conditions to so alter the normaldivision of current between the two parallel paths that a considerableaugmented heating eiect is produced. Such an arrangement is especiallysuitable for use with higher current circuits wherein the problems oflarge biasing forces and corona become particularly severe.

The disk 15 is adapted to close the lower end of each type of rell unit,and since the passage 63 through the ierrule 44 is substantially thesame diameter as the disk, it offers no impedance to the outwardlyflowing arc extinguishingl gas during the operation of the device, thedisk being held in position by the same fusible element which causes theoperation of the breaker.

The fuse is shown in the closed circuit position in Fig. l, and it willbe noted that the main operating spring I9 is tensioned so as to biasthe piston member 33 in the direction of the upper terminal member 1.This biasing force is transmitted through the plunger and must beentirely balanced by the fusible element 61. Upon the occurrence of anoverload condition in the controlled circuit of sucient magnitude andduration to cause the heat generated in the disk member 15 andtransmitted to the fusible element 61 by means of the retaining rivet 1Ito effect the fusing of that element, the lower end of the plunger 41 isreleased and that member is caused to move upwardly into the central arcpassage45 under the biasing action of the operating spring I9. An arc isimmediately established between the lower end of the plunger 41 and theferrule 44. This arc will practically instantaneously contact the lowerend of the wire 85 thereby putting the conductors 83 and 85 within thesmaller arc passage 49 in parallel with the arc. If the current to beinterrupted is of small magnitude, the immediate result will be anextinction of the arc in the central passage at the first zero point,all of the current owing through the conductors 83 and 85. Furtherupward movement of the plunger 41 will then result in a separation ofthe two wires 83 and 85 which are in slidable conductive relationship,and a second arc will be established within the smaller arcextinguishing passage 49. That passage is particularly adapted forextinguishing small arcs, and the outowing superheated water vapor willcause a rapid cooling and extinguishing of the arc.

If the magnitude of the arc current is large it will cause an immediatefusing of the conducting means (the wires 83 and 85) within the smallerarc passage 49, and the arc will persist in the larger passage 45,although the extinguishing operation is essentially the same. The heatof the arc causes the boric acid lining 43 to evolve superheated steamwhich flows outwardly longitudinally of the arc through the throatopening 55, the opening 63 in the ferruie, and the continuation of thatopening in the lower portion of the terminal member 9 and the hollowcylindrical member 91. The disk member 15 is blown out of the openingthrough the lower end of the fuse tube immediately upon the generationof any appreciable gas pressure within the device.

The provision of two arc passages and means for establishing an arc ineach of those passages is an important feature of my invention insecuring satisfactory operation of the device over a Wide range of arccurrents. This results from the fact that a suiilcient evolution of arcextinguishing gas from the boric acid lining member of the two arcpassages is secured only when the arc is brought into intimate contactwith the inner surface of those passages. Thus if a low current arc weredrawn into the larger of the arc passages, it would probably exist foran indefinite period of time due to the fact that insuflicient gas wouldbe evolved to eiiect its extinguishment. And while satisfactoryinterruption of low current arcs is secured within a small diameter arcpassage, it is impossible to secure satisfactory interruption of heavycurrent arcs in such a passage, due to the fact that there isinsufficient cross sectional area to permit all of the generated gas tovent without building up pressures within the passage capable of causingsevere damage to the entire device.

The operation of Y the modification shown in Fig. 3 is essentially thesame as the operation of the structure shown in Fig. 2, except that thefirst step in the circuit interrupting operation is the fusing of thelink 95 which is connected in parallel with the current-carrying heater(the disk 15). The fusion of this link 95 causes substantially all ofthe current flowing through the interrupter to flow through the heaterdisk 15. thereby greatly increasing the internal heating producedtherein. 'Ihis additional heat is practically immediately transmitted tothe fusible element 61 by means of the plunger retaining rivet 1I andcauses the fusing of the junction between that member and the fusibleelement itself, thereby permitting the operating spring I9 to move theplunger to the open circuit position.

Following each circuit interrupting operation of the fuse, it isnecessary to restore the device to anoperative condition. 'Ihis isaccomplished, in the preferred embodiment of my invention, by thereplacing of the refill element 31 therebyrenewing all of the parts ofthe fuse which come in contact with the arc and which may be damagedthereby. The reilll element 31 is relatively inexpensive, however, dueto its simple structure, and while it makes possible the restoration ofthe fuse to a potential eiectiveness equal to. that when new, the costof so doing is much less than the cost of restoring any of thepreviously known high-interrupting-capacity high-voltage fuses to anoperative condition.

In the open circuit position, the plunger member 41 has been moved bythe operating spring |99. suihcient distance to draw the lower end ofthe plunger to the top of the central arc extinguishing passage 45. 'Iherst step in the insertion of a new refill element consists in theunscrewing of the threaded annular retaining member 91 which engages thethreaded portion 96 of the lower terminal member 9. The ilbre tube 4Iwhich forms the body portion of the rell ele- 5 ment 31 and its attachedferrule 44 are then free to drop out leaving only the plunger 41 withinthe fuse tube I. In order to remove the plunger and re-insert the newrell element, the cap member 2I on the upper terminal 1 is unscrewed,move- 75 ment of the upper support member 21 being prevented by the pin99 which engages suitable slots (not shown) in the annular member I1.'I'he upper supporting member 21, the operating spring I9, the pistonmember 33, and the plunger member 41 are then free to drop out the-lowerend of the tube.

The next step is the unscrewing of the plunger member 41 from the pistonmember 33. Following this, a new refill element 31 is screwed securelyintothe piston member 33, the pin 19 preventing rotation of the plunger41 with respect to the body portion of the refill element. The connectedrefill element and the plunger mechanism are then inserted in the lowerend of the tube I, and the cylindrical retaining member 91 is tightenedso as to securely hold the ferrule 44 of the rell element 31 against thecooperating annular shoulder I0l of the lower terminal 9. In order totension the spring I9, it is necessary to insert a, means for engagingthe spring supporting member 21 into the fuse through the opening in theupper annular portion I1, the simplest device for effecting this being arod having a suitable threaded end for engaging the threaded hole |03 inthe top of the supporting member 21. 'I'his rod or other means isscrewed into the threaded opening i03 and the spring supporting member2l is then pulled upwardly. toward the top terminal member ii. The pin99 is alined with the means which prevents the upper support member 2lfrom turning with respect to the tube itself, and this means also servesto hold the support member in the upper position while the cap member 2lis screwed on. The upper portion of the fuse tube is thus effectivelyclosed and the entire device has been restored to an operativecondition.

Particular attention is directed to the physical dimensions of thefusible element and the heater means therefor. Both are of such sizethat injurious corona formation will not occur at the voltages of thecircuits on which these devices are ordinarily used, and in addition,the heater-fuse combination possesses suflicient thermal capacity topermit the device to carry heavy overload currents for short periodswithout in any way decreasing the ability of the device to function uponthe occurrence of prolonged low current overloads.

It will thus be seen that I have disclosed an improved high voltageexpulsion fuse which is particularly suitable for use on very highvoltage circuits through which low magnitude currents normally flow.

In addition, it will be seen that I have disclosed an improved refillelement for use with expulsion fuses which permits the replacement, at avery moderate cost, of all of the parts of the fuse which are exposed tothe action of the arc. Further, I have disclosed means whereby a fusibleelement possessing considerable mechanical strength and suiiicient largephysical dimensions to prevent any injury thereto as a result of coronaformations may be utilized on very low current circuits.

Besides these features capable of wide adaptation to the expulsion fuseart, I have disclosed certain specific forms of construction which areparticularly effective in carrying out the general objects of myinvention. One of these forms is an improved heater means for thefusible element of a circuit interrupter which utilizes a currentcarrying element of non-metallic resisting material and conducting meansin intimate contact therewith for transmitting the heat generated to thefusible element.

Another of these improved forms is a heater for a thermally responsivefusible element which utilizes a current carrying electro-responsi"edevice in parallel with the heater for increasing the normal heatingeffect thereof upon the occurrence of predetermined conditions.

While, in accordance with the patent statutes, I have given theforegoing details of a preferred practical embodiment of my invention,it is to be understood that many variations from the precise formdescribed are possible and may for some applications be desirable. Idesire, therefore, that the language of the accompanying claims shall beaccorded the broadest reasonable construction and that my invention belimited only by what is explicitly stated in the claims and by the priorart.

I claim as my invention:

l. In a circuit interrupter, means for defining the walls of an arcchamber, a rigid plunger means movable within said arc chamber to aclosed circuit position and to an open circuit position, means biasingsaid plunger means toward the open circuit position, thermallyresponsive means for restraining said plunger means in the closedcircuit position, against said biasing means, and means for heating saidthermally responsive means comprising a current carrying heater and anelectro-responsive means for limiting the current in said heater exceptupon the occurrence of predetermined electrical conditions.

2. In a circuit interrupter, means for defining the walls of an arcchamber, conducting means movable within said arc chamber to a closedcircuit position and to an open circuit position, spring means biasingsaid movable means toward the open circuit position, thermallyresponsive means for restraining said movable means in the closedcircuit position against said biasing means, and heater means forcausing said thermally responsive means to release said movable means,said heater means comprising a currentcarrying heater unit and acurrent-carrying electro-responsive unit, normally connected in parallelwith said heater unit, for limiting the current flow in said heater unituntil the occurrence of predetermined electrical conditions.

3. In a circuit interrupter, means for defining v the walls of twoconnecting chambers, means movable Within one of said chambers to aclosed circuit position and to an open circuit position, spring meansdisposed within the other of said chambers for biasing said movablemeans toward the open circuit position, fusible thermally responsivemeans for restraining said movable means in the closed circuit positionagainst said biasing means, and heater means for causing the release ofsaid movable means, said heater means comprising a current-carryingheater unit, and a current-carrying fusible element, normally connectedin parallel with saidheater unit, for limiting the current iiow in saidheater unit until the occurrence of predetermined electrical conditions.

4. In a circuit interrupter, tubular means for defining the walls of anarc chamber, a rigid plunger means movable Within said arc chamber to aclosed circuit position and to an open circuit position, means biasingsaid plunger means toward the open circuit position, fusible thermallyresponsive means disposed within said arc chamber for restraining saidphmger means in the closed circuit position against said biasing means,and means for heating said fusible means comprising a current-carryingheater unit and a current-carrying electro-responsive unit connected in-parallel with said heater means, said electro-responsive unit operatingupon the occurrence of predetermined conditions to cause an increase inthe normal heating effect of said heater unit.

5. In an electro-responsive device, a fusible element and a heater meanstherefor comprising a current carrying body of non-metallic resistancematerial, means extending through said body for conducting the heatgenerated therein to said fusible means, and a current-carryingelectroresponsive means connected in parallel with said current-carryingbody of resistance material, said electro-responsive means acting uponthe occurrence of predetermined conditions to so change the normaldivision cf current iiow between said parallel paths so that asubstantially greater than normal proportion of the current ows throughsaid resistance unit.

6. In an electro-responsive device, a fusible element, and a heatermeans therefor comprising a current-carrying body of non-metallicresistance material, means vextending through said body for conductingthe heat generated therein to said fusible means, and a current-carryingfusible means connected in parallel with said current-calrying body ofresistance material, said means being fusible upon the occurrence ofpredetermined conditions to cause substantially all of the currentflowing through said device to iiow through said body of resistancematerial.

'7. In a circuit interrupter, tubular means at least partially ofinsulating material, a cap means of conducting material for closing oneend of said tubular means, a means of conducting material supported atthe other end of said tubular means in such manner that at least aportion of the central passage through said tubular means will be open,means supported on said cap means and movable within said tube to openthe circuit, means biasing said movable means to the open circuitposition, and means for retaining said movable means in the closedcircuit position against said biasing means, said retaining meanscomprising a fusible means, and a member of non-metallic resistancematerial which is adapted to be held against said tube and saidconducting means by said biasing means in such manner that said tube isreleasably closed when said interrupter is in the closed circuitposition.

8. In a circuit interrupter; tubular means, at least partially ofinsulating rmaterial; conducting means supported adjacent one end dfsaid tubular means; fusible means within said tubular means; and meansfor ,substantially closing one end of said tubular means and forelectrically connecting said fusible means with said conducting means,said means comprising a heater means for causing the fusion of saidfusible mea-ns upon the occurrence of predetermined conditions, andhaving proper dimensions for closing one end of said tubular means; saidconnecting means being normally retained in position by, said fusiblemeans but being movable upon the fusion of that means to open one end ofsaid tubular means.

9. In a circuit interrupter; tubular means for defining an arc passage,at least a portion of which is lined With a material capable of evolvingan arc extinguishing gas when placed in proximity to an electric arc;conducting means movable through said arc passage to establish an arctherein; fusible means for controlling the operation of said arc drawingmeans; and heater means for causing the fusion of said fusible meansupon the occurrence of predetermined conditions, said heater means beingnormally adapted to close one end of said arc passage and being movable,during the circuit interrupting operation, to open at least a portion ofone end of said arc passage in order to permit the venting of the gasevolved from said lining.

l0. In a circuit interrupter; tubular means for defining an arc passage,at least a portion of which is lined with a material capable of evolvingan arc extinguishing gas when placed in proximity to an electric arc;conducting means movable through said arc passage to establish an arctherein; fusible means for controlling the operation of said arc drawingmeans; and heater means for Causing the fusion of said fusible meansupon the occurrence of predetermined conditions, said heater meanscomprising a member of nonmetallic, resistance material which is soproportioned that it normally closes one end of said arc passage andwhich is movable, during the circuit interrupting operation, to open oneend of said arc passage in order to permit the venting of the l gasevolved from said lining.

1l. In a circuit interrupter; tubular means for defining an arc passage,at least a portion of which is lined with a material capable of evolvingan arc extinguishing gas when placed in proximity to an electric arc;means for closing one end of said tubular means; spring biased,conducting means movable through said arc passage to establish an arctherein; fusible means for preventing movement of said arc drawing meansexcept upon the occurrence of predetermined conditions; and acurrent-carrying heater means, lthermally conductively disposed withregard to said fusible means, for causing the fu.'- sion thereof uponthe occurrence of predetermined conditions; said heater means being soproportioned that it normally closes one end of said arc passage, beingheld in that position by said spring biased, arc drawing means, andbeing movable, during the circuit interrupting operation, to open oneend of said passage in order to permit the venting of the gas evolvedfrom said lining.

12. In an expulsion circuit interrupter;` tubular means for defining anarc passage, at least a portion of which is lined with a materialcapable of evolving an arc extinguishing gas when placed in proximity toan electric arc; means for closing one end of said arc passage, theother end of said arc passage being open during the circuit interruptingoperation; a spring biased, plunger means movable through said arcpassage to establish an arc therein; fusible means for normallyrestraining said arc drawing means in the closed circuit position; andcurrent-carrying heater means for causing the fusion of said fusiblemeans upon the occurrence of predetermined conditions; said heater meanscomprising a substantially non-inductive resistance element, being 'soproportioned that it substantially closes said other end of said arcpassage, except during the circuit interrupting operation, being held inthat position by the reaction forces exerted by said spring biasedplunger, and being adapted to be moved in the opposite direction to thatin which said arc drawing plunger is moved, during the circuitinterrupting operation, by the gas evolved from said lining; saidmovement of said heater means causing said other end of said arc passageto be opened so as to permit substantially free venting of said gas.

13. In a circuit interruptor; tubular means for denning an arc passage;means for closing one end of said arc passage; a conducting seatpositioned at the other end of said passage; means, including a springbiased fusible element, for drawing an arc within said arc passageduring the circuit interrupting operation; and a substantiallynon-inductive, current-carrying, heater means for causing the fusion ofsaid fusible element upon the occurrence of predetermined conditions,said heater means including a member of non-metallic resistance materialwhich is held against said seat by the reaction forces of said springbiased arc drawing means.

14. In a circuit interrupter; tubular means for defining an arc passage;means for closing one end of said arc passage; a conducting seatpositioned at the other end of said passage; means, including a springbiased fusible element, for drawing an arc within said arc passageduring the circuit interrupting operation; and a substantiallynon-inductive, current-carrying, heater means for causing the fusion ofsaid fusible element upon the occurrence of predetermined conditions,said heater means including a member of non-metallic, resistancematerial, having a passageway therein, which is adapted to be held againsaid seat by the reaction forces of said spring biased arc drawingmeans, said reaction forces being transmitted to said resistance memberthrough the agency of a conducting means, having an enlarged headportion, which means extends through said passageway and serves toconduct the heat generated within said resistance element to saidfusible arc drawing means.

i5. In a circuit interrupter, conducting means movable from a closedcircuit position to an open circuit position to open the electricalcircuit through said interrupter, means biasing said movable means tothe open circuit position, and electro-responsive means for normallyholding said movable means in the closed circuit position against saidbiasing means, said holding means including a fusible element, heatermeans for said fusible element comprising a hollL-w member of resistancematerial, and a means of conducting material which extends through saidhollow heater member for mechanically 'and thermally connectingv saidfusible element and said heater, said means of conducting materialhaving an enlarged head portion for engaging said heater, and both saidfusible element and said heater being subjected to substantially all theforce of said biasing means.

16. In a. circuit interrupter, conducting means movable from a closedcircuit position to an open circuit position to open the electricalcircuit through said interrupter, tension spring means biasing saidmovable means to the open circuit position, and electro-responsive meansfor normally holding said movable means in the closed circuit positionagainst said biasing means, said holding means including a fusibleelement, -heater means for said fusible element comprising a hollowmember of non-metallic resistance-material, means for supporting saidheater member, and a rod-like member of conducting material whichextends through said hollow heater member for mechanically and thermallyconnecting said fusible element and said heater, said rod-like memberhaving an enlarged head portion for engaging said heater, and both saidfusible element and said heater being subjected to substantially all theforce and of said biasing means.

17. In a circuit interrupter, tubular means for defining an arc passage,a seat positioned at one end of said tubular means, means movable from aclosed circuit position to an open circuit position to open theelectrical circuit through said interrupter and establish the arcincident thereto within said arc passage, means biasing said movablemeans to the open circuit position, electro-responsive means including afusible element for normally holding said movable means in the closedcircuit position against said biasing means, and a heater means forcausing the fusion of said fusible element upon the occurrence ofpredetermined conditions, said heater means including a member ofresistance material which is held against said seat by the reactionforces of said biasing means.

18. In a circuit interrupter, tubular means for defining an arc passage,a conducting seat positioned at one end of said tubular means, meansmovable from a closed circuit position to an open circuit position toopen the electrical circuit through said interrupter and establish thearc incident thereto within said arc passage, means biasing said movablemeans to the open circuit position, and electro-responsive means fornormally holding said movable means in the closed 'circuit positionagainst said biasing means, said holding means including fusibleelement, heater means for said fusible element comprising a hollowmember o resistance material, and a means of conducting material whichextends through said hollow heater means for mechanically and thermallyconnecting said fusible element and said heater, said heater means beingadapted to engage said seat and being normally held against said seat bythe reaction force of said biasing means which force is transmittedthereto by said means of conducting material.

19. In a circuit interrupter, tubular means for defining an arc passage,a conducting seat positioned at one end of said tubular means,conducting means movable from a closed circuit position to an opencircuit position to open the electrical circuit through said interruptorto establish the arc incident thereto within said arc passage, resilientmeans biasing said movable conducting means to the open circuitposition, and electro-responsive means for normally holding saidconducting means in the closed circuit position against said biasingmeans, said electroresponsive means including a fusible element, heatermeans for said fusible element comprising a`hollow member ofnon-metallic resistance material, and a means of conducting materialhaving a body portion which extends through said hollow heater means formechanically and thermally connecting said heater and said fusibleelement, at least the edge portions of said heater member engaging saidconducting seat, said means of conducting material having an enlargedhead portion for engaging said heater adjacent the central openingtherethrough, and said heater being held in engagement with saidconducting seat by the reaction force of said resilient biasing meanswhich force is transmitted thereto by said means ofv conductingmaterial.

HERBERT L. RAWLINS.

